Description
Inefficient algorithmic complexity in the JSON reader of Progressive Robot hMailServer allows a remote unauthenticated attacker to make the mail services unavailable. Reading a JSON object kept the first of each duplicated member name by searching the members already read, so an object of N distinct member names cost O(N^2): 1 MB took 8.9 seconds and 4 MB took 300 seconds against the affected code. A remote attacker reaches the reader without an account by mailing a crafted TLS-RPT report (up to 16 MB after decompression) to a hosted domain's published report mailbox, which is read on a delivery thread; a few such reports hold every delivery thread (ten by default), so the server delivers no mail, local or outbound, for over an hour per report. A signed-in account reaches the same 16 MB body through the webmail's own REST routes, holding the REST API's own worker threads. Where no report mailbox is configured, the unauthenticated REST sign-in routes that read a JSON body are capped at 64 KB and are not affected.
Published: 2026-10-08
Score: 7.5 High
EPSS: < 1% Very Low
KEV: No
Impact: Remote Denial of Service
Action: Patch Now
AI Analysis

Impact

Inefficient JSON parsing in hMailServer causes a quadratic time complexity when handling objects with duplicate member names. An attacker can craft a 16 MB JSON payload and deliver it via a TLS‑RPT report or the webmail REST API, forcing the server to search already‑read members and consuming a delivery or API worker thread for minutes. Because the processing thread remains busy, the server stops delivering any mail, both inbound and outbound, for an hour per report, effectively denying service to all users.

Affected Systems

All versions of Progressive Robot Ltd.’s hMailServer released before 6.3.6 contain the flaw; the patch in 6.3.6 keeps member names in a hash set and parses JSON in one pass. The vulnerability affects any hosted domain that has TLS‑RPT reports enabled and any webmail REST endpoint that accepts JSON bodies larger than 64 KB.

Risk and Exploitability

The CVSS score of 7.5 denotes a high impact denial‑of‑service scenario. EPSS is not available, but the exploit requires only a crafted email or REST request, no authentication, and can be performed remotely. The flaw is not listed in the CISA KEV catalog, yet the risk remains significant for organizations that rely on TLS‑RPT reports or the REST API for mail handling.

Generated by OpenCVE AI on October 8, 2026 at 13:25 UTC.

Remediation

Vendor Solution

Upgrade to hMailServer 6.3.6, which keeps the member names seen in a hash set, so a JSON object is read in one pass. Until then, where domain reports are on, move the report mailbox off a hosted domain; restart the service to end a busy thread.

OpenCVE Recommended Actions

  • Upgrade to hMailServer 6.3.6.
  • If upgrading is delayed, move the TLS‑RPT report mailbox off a hosted domain and restart the service to clear the occupied thread.
  • Disable TLS‑RPT reporting or impose a strict size limit on JSON payloads that the server parses.

Generated by OpenCVE AI on October 8, 2026 at 13:25 UTC.

Tracking

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Advisories

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History

Fri, 09 Oct 2026 07:30:00 +0000

Type Values Removed Values Added
First Time appeared Progressive Robot
Progressive Robot hmailserver
Vendors & Products Progressive Robot
Progressive Robot hmailserver

Thu, 08 Oct 2026 15:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Thu, 08 Oct 2026 12:00:00 +0000

Type Values Removed Values Added
Description Inefficient algorithmic complexity in the JSON reader of Progressive Robot hMailServer allows a remote unauthenticated attacker to make the mail services unavailable. Reading a JSON object kept the first of each duplicated member name by searching the members already read, so an object of N distinct member names cost O(N^2): 1 MB took 8.9 seconds and 4 MB took 300 seconds against the affected code. A remote attacker reaches the reader without an account by mailing a crafted TLS-RPT report (up to 16 MB after decompression) to a hosted domain's published report mailbox, which is read on a delivery thread; a few such reports hold every delivery thread (ten by default), so the server delivers no mail, local or outbound, for over an hour per report. A signed-in account reaches the same 16 MB body through the webmail's own REST routes, holding the REST API's own worker threads. Where no report mailbox is configured, the unauthenticated REST sign-in routes that read a JSON body are capped at 64 KB and are not affected.
Title Inefficient Algorithmic Complexity in hMailServer
Weaknesses CWE-407
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

Subscriptions

Progressive Robot Hmailserver
cve-icon MITRE

Status: PUBLISHED

Assigner: GitLab

Published:

Updated: 2026-10-08T14:15:58.279Z

Reserved: 2026-10-08T10:51:35.642Z

Link: CVE-2026-107574

cve-icon Vulnrichment

Updated: 2026-10-08T14:15:54.649Z

cve-icon NVD

Status : Deferred

Published: 2026-10-08T12:17:15.177

Modified: 2026-10-08T21:02:43.860

Link: CVE-2026-107574

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-10-09T07:15:09Z

Weaknesses
  • CWE-407

    Inefficient Algorithmic Complexity